Ron - will this be a dive trip? I'm usually up for that.

No, fishing and socializing with a friend.

I think the gas alone is more than $215 US from San Pedro. The fare RT does not sound right - maybe they are taking you to a different long caye -!

There is a Long Caye south of Caye Chapel.
I've heard many times 'In Belize if they don't know the name of an island they call it 'Long Caye'.
I also read there are more than 1000 islands off the coast of Belize and its associated atolls.

Even though my husband included "Long Caye at Lighthouse Reef" in the subject line of all emails back/forth, he found out this afternoon that the taxi company was referring to a different Long Caye.

So, we are back to trying to find something reasonable. I'm ready to say forget the property @ Long Caye and let's just spend the entire day at Ambergris.

I honestly think that the US$600 you were originally quoted is about right. If you manage to get it for less it won't be much less. Bear in mind that this will be the cost each time you want to go back and forth, unless you get your own boat. And don't underestimate the costs of getting and operating/maintaining a suitable boat.